The melting point of a substance is the temperature at which that substance starts changing from the solid phase to the liquid phase. At this temperature, the liquid and solid phases are in equilibrium. With additional heat, the substance will melt completely. But what determines a substance’s melting point? Let’s think about solids and liquids. A solid’s molecules hold each other in a rigid, ordered structure called a lattice, while a liquid’s molecules have weaker interactions and move around.
Heating a solid transfers energy to the molecules. With enough energy, the molecules overcome the forces keeping them in the lattice and start moving around. In other words, if we heat a solid enough, it melts into a liquid. So, the melting point depends on the energy it takes to overcome the forces between the molecules, or the intermolecular forces, holding them in the lattice. The stronger the intermolecular forces are, the more energy is required, so the higher the melting point is.
Many intermolecular forces depend on how strongly atoms in the molecule attract electrons — or their electronegativity. Nitrogen, oxygen, fluorine, and chlorine are highly electronegative, while carbon, hydr
